Electric discharge device of the magnetron type



R. J. BoNDLl-:Y

Nov, 16, 1948.

ELECTRIC DISCHARGE DEVICEOF THE MAGNETRON-TYPE Filed Ju]`.y'29, 1944 Ill.

- "Inventor: Y

Ralph JBOndIey, y

vll/lill. vl

'Il lll/lll Patented Nov. 16, i948 ELECTRIC DISCHARGE DEVICE F THE MAGNETRON TYPE Ralph Si'. Bondley, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application July 29, 194i, Serial No. 547,155

(Cl. S- 40.)

4i Claims.

My invention relates to improvements in electric discharge devices and more particularly to an improved cathode construction particularly applicable to electric discharge devices of the magnetron type.

My invention relates particularly to magnetrons of the type described and claimed in the copending application of E. D. McArthur, Serial No. 447,903, filed June 22, 1944, now Patent 2,412,824 dated December 17, 1946, and assigned to the assignee of the present application. The said McArthur application is prior art with respect to my invention.

In certain magnetron constructions the pole faces of the magnets are positioned close to the interelectrode space to make e'ective use of the available magnetomotive force. In some of these constructions, the pole faces are at the potential of the anode structure, and it is necessary to provide some shielding means to prevent the electrons from the interelectrode space from being collected on the pole faces. Shield members connected with the cathode have been provided for this purpose. In prior art constructions, such as the one described above, the operating efficiency has sometimes been less than expected and tubes which are mechanically identical exhibit very different electrical characteristics. I have found that low eiciency and variable electrical characteristics are attributable largely to the emission of electrons by the end shields which do not contribute to the rotating space charge in the interelectrode space. In accordance with the present invention, I provide an improved magnetron construction in which these undesirable characteristics have been eliminated by preventing electron emission from the end shields.

It is an object of my invention to provide a new and improved electric discharge device.

It is another object of my invention to provide a new and improved cathode and end shield construction particularly adapted for use in electric discharge devices of the magnetron type.

In accordance with the illustrated embodiment of my invention an electric discharge 'device of the magnetron type is provided with an anode structure which defines a substantially cylindrical space lsurrounded by a plurality of smaller cylindrical spaces communicating with the rst mentioned space by radially extending slots. generally cylindrical cathode is supported inV the central cylindrical space del-ined by the anode structure and provides a source of electrons in the interelectrode space. The anode andv cathode are mounted within an envelope which also Cil supports a pair of` permanent magnet members having pole faces adjacent the opposite ends, of the interelectrode space. In order to prevent electrons from being collected by the pole faces which are maintained at the direct current voltage of the anode structure during operation of the device, shield members are provided on the ends of the cathodes of substantially larger diameter than the cathode proper. The shields are secured to outwardly extending flanges on the cathode sleeve and maintaine lin spaced relation with respect thereto by a plurality of short lengths of nickel wire which are interposed between the flanges and the end shields and spot welded thereto. The end shields are formed* ci a material which is a poor electron emitter, such as nickel, and are blackened to improve the heat radiating properties thereof so that they operate at a low temperature. With this construction, end shield emission is substantially eliminated and the operatingcharacteristics and efciency of the device are greatly improved.

For a better understanding of my invention, reference may be had to the following description taken in connection with the. accompanying drawing, andits scope will be pointed out in the appended claims. Fig. 1 is an elevational view, in section, of an electric discharge device. of the magnetron type embodyingmy invention; Fig. 2 is a sectional View taken along the line 2-2 of Fig. l; Fig. 3 is an enlarged elevational; view, in section, showing the details of construction of my improved cathode and end shields, and Fig. 4 is a sectional View taken along the line 4.-,-4 of Fig. 3.

Referring particularly to Fig l, there is shown an elongated cylindrical container, the lateral wall structure of which is provided by a single metal tube I consisting of ferromagnetic material such as cold rolled steel or the like. The ends of the container are closed by` flanged members 2 and 3 which are welded or otherwisehermetically joined to the inner surface of theA part l'. The outer surface oi the envelope is provided with a series of circumferentially extendingl 4 which serve as heat dissipating elements, and a somewhat larger circular element 5 is provided near the upper end of the lcontainer which acts as a mounting flange for the device as a whole.

Within the container and approximately at its central region there is an anode structure E, shown in plan view in Fig. 2. This comprises a circular member which has a relatively large centralv opening l and a series of smaller openings 8 arranged symmetrically about the lcentral openf ing. The central opening is joined to the openings 8 by means of radially extending slots 9. The structure 6, which preferably consists of copper, is supported by and brazed to the interior wall surface of the part I. To facilitate the brazing operation, small channels are cut in the outer periphery of the structure and these are used to receive rings of the brazing material applied before the anode structure is inserted within the container. A relatively large circumferentially extending channel II serves to reduce the overall weight of the structure.

A magnetic eld is provided in the central opening 1 of the anode structure by a pair of magnetic members |2 and I3 supported, respectively, from the flange members 2 and 3. The members I2 and I3 may to advantage be formed of permanent magnet material having a high coercive force and a high energy factor, such as alnico. The magnetic members I2 and 3 are secured in desired positional relationship with respect to the anode structure by disks I4 and I5 which are spaced from the anode structure by cylindrical sleeves I6. The magnetic members I2 and I3 are preferably provided with axially extending centrally located passageways I1 and I8. The passageway I8 terminates in an exhaust tubulation |9 and the passageway I1 terminates in a seal including a body of glass 20 through which the conductors 2| and 22 are sealed. Conductor 2| is connected with a hollow cylindrical conductor 23 which extends through the passageway I1 and supports a generally cylindrical cathode 24 centrally in the enlarged opening 1 of the anode structure. As shown more plainly in Fig. 3, the conductor 22 extends into the cathode 24 and provides a lead-in conductor and support for the lower end of a lamentary heater 25. The conductor 22 is spaced and electrically insulated from the cylindrical conductor 23 by a plurality of insulating spacers 26 (only one of which is illustrated in the drawing). The outer conductor 23 is spaced from the walls of the passageway |1 by an insulator 21 which is shaped to provide long leakage paths between the magnetic member I2 and the outer conductor 23. tric lead-in conductor arrangement described above are described in more detail and claimed in the copending application of E. D. McArthur, Serial No. 481,840, led April 5, 1943, and now abandoned, and assigned to the assignee of the present invention.

Referring now to Fig. 3, the cathode 24 comprises a cylindrical metal sleeve 28 having an electron emissive coating 28a and provided with outwardly extending flanges 29 formed on either end thereof. A shield 3U of substantially larger diameter than the sleeve 28 is provided at the upper end of the sleeve to prevent electrons from escaping from the interelectrode space and being collected by the magnetic member I2 which is at the direct current voltage of the anode 6 during operation of the device. The shield member 3B is generally cup-shaped having a flange extendingvdownwardly from the outer edge thereof and is secured to the flange 29 and maintained in spaced relation with respect thereto by a plurality of metallic spacers which as illustrated may be short lengths of nickel wire 3| which are interposed between the shield 3D and the ilange 29. The parts 29, 30 and 3| are secured together in any desired way, such as by spot welding. The shield 30 is also provided with an upstanding flange 32 which receives the lower end of the Cil Certain features of the concenconductor 23 to provide a support for the cathode assembly. The cup shape of the shield provides a substantial area parallel to the anode 4, and cuts down emission which might result from high voltage gradient at the edges of a relatively thin plate. A similar shield 33 without the flange 32 is provided at the lower end of the cathode and is secured to the lower flange 29 in the same manner as shield 30 is secured to the upper ange. As clearly shown in Fig. 4, three metal members or pieces of wire 3| are provided for making the connection between the shields and the flanges 29. This construction maintains the shield members 3l) and 3| at the potential of the cathode so that they provide an effective electrostatic shield between the interelectrode space and the ends of the magnet members I2 and I3. The very limited cross sectional area of the connecting members 3| minimizes the transfer of heat between the cathode structure and the end shields so that the shields remain at a relatively low temperature during operation of the device. The temperature of these shields may still further be reduced by carbonizing them to improve their heat radiating properties. By the reduction in operating temperature of the shields together with the utilization of a material which is a poor electron emitter, such as nickel, the emission of electrons external to the interelectrode space is substantially eliminated.

Although the operation of the illustrated embodiment of my invention is believed to be well understood by those skilled in the art, it may be briefly described as follows: Electrons emitted from the surface of the cathode 24 move in curvilinear paths in the interelectrode space under the combined action of the magnetic field produced by the members l2 and I3 and an electric field produced by the voltage applied between the conductor 2| and the anode 6. The resultant motion of the electrons excites the anode structure at a frequency determined by the geometry of the openings 8 and connecting slots 9. High frequency energy may be extracted from the device by a loop conductor 34 having an enlarged portion 35 extending from the envelope I and hermetically sealed thereto by a body of glass 36 interposed between the conductor 35 and a sleeve 31 surrounding the conductor 35. Conductor 35 and sleeve 31 may be coupled to the central and outer conductors of a high frequency transmission system.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modilications may be made without departing from my invention in its broader aspects, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device of the magne tron type including an anode structure having an opening therein, a cathode mounted within said opening, magnetic means electrically connected to said structure including a pole face adjacent said opening for producing a magnetic field in the space between said anode structure and said cathode, a metallic shield of material which is a poor electron emitter and having a blackened surface which enhances thermal radiation, said shield being positioned transversely with respect to a path of electrons leaving said opening and conductively connected to said cathode, said shield having a iianged portion extending from its periphery in a direction toward said cathode whereby voltage gradients in the vicinity of the periphery of said shield are minimized.

2. An electric discharge device of the magnetron type including an anode structure having a cylindrical opening therein, a cathode structure comprising a generally cylindrical sleeve having an electron emissive coating co-axially positioned within said cylindrical opening, magnetic means electrically connected to said structure including a pole face adjacent one end of said opening for producing a magnetic eld in the space between said structure and said cathode, a metallic end shield of material which is a poor electron emitter having a diameter substantially larger than said sleeve and being positioned transversely of the axis thereof, a plurality of spaced circumferentially positioned metallic wires between said shield and the end of said cylindrical sleeve, said wires conductively connecting said shield to said sleeve and forming a path of high resistance to the flow of heat therebetween, said shield having a blackened surface which enhances thermal radiation.

3. A discharge device as in claim 2 wherein said shield has a flange portion extending about its periphery and toward said sleeve whereby voltage gradients in the vicinity of said periphery may be minimized.

4. An electric discharge device of the magnetron type including an anode structure having a cylindrical opening therein, a cathode structure including a generally cylindrical sleeve coaxially positioned within said cylindrical opening, magnetic means supported in insulated relation with respect to said cathode and including a pole face adjacent one end of said opening for producing a magnetic iield in the space between said structure and said cathode, a metallic end shield of material which is a poor electron emitter having a diameter substantially larger than said sleeve and being positioned transversely 0f the axis thereof, a plurality of circumferentially spaced metallic connecting means between said shield and the end of said cylindrical sleeve, said metallic conducting means conductively connected t0 said shield and to said sleeve and forming a path of small heat transfer capacity therebetween to thereby minimize thermionic emission of electrons by said shield, which may be collected on said pole face.

RALPH J. BONDLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,002,667 Knoll May 28, 1935 2,233,917 De Boer et al Mar. 4, 1941 2,406,276 White Aug. 20, 1946 2,408,239 Spencer Sept. 24, 1946 FOREIGN PATENTS Number Country Date 215,600 Switzerland Oct. 16, 1941 509,102 Great Britain July 11, 1939 

